Project case: tank cleaning on petrochemical site

Removal of flash rust on the inside of a tank

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Title

Problem description

Formation of flash rust after high-pressure water blasting


At a large asset downer in the petrochemical industry, Ethylene Oxide (EO) is stored in various buffer tanks. This EO serves as a raw material for their further production and has a number of special properties: it is highly toxic in its liquid state and extremely explosive in its gaseous state. Another special property is that the presence of oxides acts as a catalyst for the formation of polymer. If this process reaches a certain critical point, this reaction is unstoppable. This is the core of the cleaning problem.


If polymer starts to form, which is always the case after a certain period of time, the tank has to be emptied and the tank is completely cleaned to remove all polymer. This is done by high-pressure water blasting (more specifically 'buttering' or high-pressure cleaning with a butterhead). After this high pressure water blasting, a layer of flash rust forms on the walls. In other words, an oxide layer that acts as a catalyst for polymerisation. This layer has to be removed as well.

Previous solutions

Abrasive techniques with secondary waste



In the past, abrasive blasting methods were mainly used to remove the flash rust. Firstly with classical grit blasting, secondly with sponge blasting. This gives rise to three additional problems:

  • need for (complete) removal of the grit 
  • dust generation - need for confinement
  • the reappearance of rust almost immediately after the blasting process, which results in an enormous time pressure to place the tank in nitrogen condition.


Challenges in the project

Assignment is located in the middle of ATEX area



The project includes some specific challenges:

  • the tank is located in an ATEX zone
  • the asset-owner has never used laser cleaning as a cleaning method.
  • Netalux does not have a reference case it can rely on to estimate efficiency and timing
  • it is not known if there is still EO in the pores of the tank
  • work has to be done at different levels in the tank because not everything is accessible at man height
  • ergonomic conditions for performing the laser cleaning manually


Title

Regular consultation with the customer and solution-focused involvement in preparation


In order to tackle this project properly for the first time (in the meantime, we carried out this project twice), we had several consultations, both by telephone and on site with the customer. The very first things that needed to be tackled were:

  • ATEX zone
  • Approval of laser cleaning as a cleaning method in a confined space


Netalux was actively involved in these preparatory meetings on its own initiative and provided possible solutions. Eventually, an MOC (Management Of Change) for the cleaning of three tanks was issued from the customer's head office in the United States on the basis of the following measures:

  • the laser cleaning machine is placed at a height on a scaffolding in order to get out of the ATEX zoning
  • the fiber with laser head comes in at the top of the tank
  • the tank is sufficiently aerated
  • air measurements are carried out every morning to monitor the presence of EO in the tank
  • entry into the tank is allowed with a maximum of 2 persons
  • operators carry oxygen and EO measurement
  • operators wear a film badge for EO exposure
  • there is a permanent security guard at the manhole
  • the works are covered by a hot work permit
  • a scaffolding is built in the tank to first work at a height and then on the lower part
  • the laser cleaning machine is equipped with an external emergency stop which is placed with the security guard


Under these conditions, in order to validate the process, we put a first trial of 1 square meter on Thursday 28 February 2019. The conditions and the results were validated in this way, so the project was awarded and planned.


Title

Results 


Delay of rust formation after laser cleaning


Already on the basis of the first test setting it was clear that cleaning with laser was successful for this application. On 12 March 2019, the cleaned square metre was still as clean as it was immediately after cleaning. This demonstrates the success of this cleaning method. It ensures that additional maintenance jobs can be carried out and that nitrogen conditions can be maintained. Moreover, it ensures that the 'oxidizing' catalyst will be present in the tank much later than normal.


Some results of the project (that has been carried out twice in the meantime):

  • projects were carried out without incidents or accidents
  • projects were carried out without EO exposure for the operators
  • the applicability of the laser cleaning technology has been proven for the asset-owner
  • an efficiency of approx. 5 square meters per hour was achieved for this manual lasering.
  • the site was able to significantly reduce the cost of cleaning its tanks


Of course, there are also points for attention:

  • air turbulence in the tank (combination extraction vs. ventilation)
  • ergonomic conditions for manual lasering
  • still room for improvement in the quality of cleaning


Customer response

Customer response


We are very pleased with this first experience with Netalux, and are planning to clean two other EO tanks in the near future to further improve the implementation of the technology. In addition to this application, the site is also looking at how it can implement laser cleaning for other applications, as it provides a unique added value: reduction of down time, cost efficiency of the project, no secondary waste, and reduced impact on nearby operations.

Title

Future


With a third tank on the MOC approval list, Netalux wants to take the next step and (semi)-automate the project. To this end, it looks at the necessary steps to be taken with the asset-owner for the deployment of a robot (arm) or possibly even a drone.